While the oils have no adverse effects, the effects of the alcohol content is controversial. Listerine contains 21% alcohol. There are some studies that suggest a link between alcohol containing mouthwashes and oral cancer. Other studies later refuted that, and officially the American Dental Association says these mouthwashes ARE SAFE.
If you are still concerned, there is an alternative. Many mouthwashes are alcohol-Free such as Listerine Zero, Crest Pro-health, Multi-Protection, and many more.